Database Design Dr. M.E. Fayad, Professor 5/18/2019 Database Design Dr. M.E. Fayad, Professor Computer Engineering Department, Room #283I College of Engineering San José State University One Washington Square San José, CA 95192-0180 http://www.engr.sjsu.edu/~fayad © 2003-2006 Dr. M.E. Fayad SJSU -- CmpE

Lesson 2: Data Modeling Using Entity-Relationship Model 5/18/2019 Lesson 2: Data Modeling Using Entity-Relationship Model 2 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

3 Lesson Objectives Understand the notation of ERDs 5/18/2019 Lesson Objectives Understand the notation of ERDs Learn how to do ER Analysis Illustrate examples for ERDs 3 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

What Is Entity-Relationship Diagrams? 5/18/2019 What Is Entity-Relationship Diagrams? E-R diagrams (ERDs): Identify major ingredients, entities, of a complicated situation Identify characteristics, attributes, of the major ingredients Uncover and analyze interconnections, relationships, among the major ingredients Assess various aspects of the relationships 4 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

What Is Entity-Relationship Diagrams? 5/18/2019 What Is Entity-Relationship Diagrams? ERD – Chen 1976 Precursor to the class diagram – Will be covered later. No generalization ERD Entities: Information holding structures Relationships: Connections between entities Cardinalities: Upper bounds Modalities: Lower bounds Attributes: Properties, characteristics, … associated with an entity. 5 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

What Is Entity-Relationship Diagrams? 5/18/2019 What Is Entity-Relationship Diagrams? In short, ERD strives to take a close look at the ingredients of a puzzle in order to identify major and minor ingredients and to figure out how they relate to each other 6 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

Entity-Relationship Diagrams 5/18/2019 Entity-Relationship Diagrams ERD can be summarized as the process of uncovering, analyzing, and explicating (i.e., stating clearly and fully) the business rules governing a complicated situation 7 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 Business Rules (1) Business rules are precise statements, derived from a detailed description of the organization's operations, that define one or more of the following modeling components: Entities Relationships Attributes Connectivities Cardinalities Constraints 1Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM 8 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

9 Business Rules (2) Examples of business rules1 5/18/2019 Business Rules (2) Examples of business rules1 An invoice contains one or more invoice lines, but each invoice line is associated with a single invoice. That is, An invoice contains one or more invoice lines. Each invoice line is associated with a single invoice. A store employs many employees, but each employee is employed by only one store. A college has many departments, but each department belongs to a single college. (This business rule reflects a university that has multiple colleges such as Business, Liberal Arts, Education, Engineering, etc.) 1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM 9 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

10 Business Rules (3) Examples of business rules1 5/18/2019 Business Rules (3) Examples of business rules1 A driver may be assigned to drive many different vehicles, and each vehicle can be driven by many drivers. (Note: Keep in mind that this business rule reflects the assignment of drivers over a period of time.) A client may sign many contracts, but each contract is signed by only one client. A sales representative may write many contracts, but each contract is written by one sales representative 10 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

11 Business Rules (4) Some business rules for a library 5/18/2019 Business Rules (4) Some business rules for a library Books and other materials exist in various editions and numbers of copies Books may or may not circulate Books that circulate may do so for varying periods Periods may be determined by Book status alone Borrower status alone Combination of book status and borrower status 11 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

12 Business Rules (5) More business rules for a library 5/18/2019 Business Rules (5) More business rules for a library Users may have various statuses Users may have varying numbers of items currently charged out to them Users may or may not owe fines Fine status may or may not affect eligibility to borrow 12 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

13 Business Rules (6) More business rules for a library 5/18/2019 Business Rules (6) More business rules for a library Staff members have attributes of Salary or wage rates Annual leave Sick leave Work schedules Job titles Special skills (e.g., languages, puppetry) Hire dates Total length of service Professional organization memberships 13 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

14 Business Rules (7) More business rules for a library 5/18/2019 Business Rules (7) More business rules for a library Physical facilities include Branches Furniture Machines (e.g., computers, microform readers, automobiles, players for CD-ROMs, audiotapes, videotapes) Library-management software Catalog records (e.g., computerized databases, catalog cards) Records of inventory, acquisitions, circulation, personnel 14 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

15 Business Rules (8) More business rules for a library 5/18/2019 Business Rules (8) More business rules for a library Related organizations may include City, university, or corporate administrations Employee unions Friends of the Library organizations Vendors of books, serials, and other products and services used by the library Networks of which the library is a member (e.g., OCLC, Amigos, Association of Research Libraries, Texas State Library network, Central Texas Library System) 15 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 E-R Diagrams (1) E-R analysis relies heavily on diagrams to represent Entities (rectangles) Attributes (ellipses) Relationships (diamonds) Connections (lines, which may have arrowheads or crowsfeet to represent degrees of connectivity or relationship) 16 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

Entity Relationship Diagrams 5/18/2019 Entity Relationship Diagrams Data models are tools used in analysis to describe the data requirements and assumptions in the system from a top-down perspective. There are three basic elements in ER models: Entities are the "things" about which we seek information. Attributes are the data we collect about the entities. Relationships provide the structure needed to draw information from multiple entities. 17 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 Developing ERDs Developing an ERD requires an understanding of the system and its components. Before discussing the procedure, let's look at a narrative created by Professor Harman. Consider a hospital: Patients are treated in a single ward by the doctors assigned to them. Usually each patient will be assigned a single doctor, but in rare cases they will have two. Heathcare assistants also attend to the patients, a number of these are associated with each ward. 18 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 Developing ERDs Initially the system will be concerned solely with drug treatment. Each patient is required to take a variety of drugs a certain number of times per day and for varying lengths of time. The system must record details concerning patient treatment and staff payment. Some staff are paid part time and doctors and care assistants work varying amounts of overtime at varying rates (subject to grade). The system will also need to track what treatments are required for which patients and when and it should be capable of calculating the cost of treatment per week for each patient (though it is currently unclear to what use this information will be put). 19 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 How do we start an ERD? (1) 1. Define Entities: these are usually nouns used in descriptions of the system, in the discussion of business rules, or in documentation; identified in the narrative (see highlighted items above). 2. Define Relationships: these are usually verbs used in descriptions of the system or in discussion of the business rules (entity ______ entity); identified in the narrative (see highlighted items above). 3. Add attributes to the relations; these are determined by the queries,and may also suggest new entities, e.g. grade; or they may suggest the need for keys or identifiers. 20 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

21 How do we start an ERD? (2) What questions can we ask? 5/18/2019 How do we start an ERD? (2) What questions can we ask? a. Which doctors work in which wards? b. How much will be spent in a ward in a given week? c. How much will a patient cost to treat? d. How much does a doctor cost per week? e. Which assistants can a patient expect to see? f. Which drugs are being used? 21 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 How do we start an ERD? (3) 4. Add cardinality to the relations Many-to-Many must be resolved to two one-to-manys with an additional entity Usually automatically happens Sometimes involves introduction of a link entity (which will be all foreign key) Examples: Patient-Drug 5. This flexibility allows us to consider a variety of questions such as: a. Which beds are free? b. Which assistants work for Dr. X? c. What is the least expensive prescription? d. How many doctors are there in the hospital? e. Which patients are family related? 6. Represent that information with symbols. 22 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

23 ERDs Overview Concepts Rules Guidelines 5/18/2019 ERDs Overview Concepts Rules Guidelines <See Documents with Lecture 04> 23 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

Crucial Use of E-R Analysis (1) 5/18/2019 Crucial Use of E-R Analysis (1) It is especially important to identify and note many-to-many (M:N) relationships: for example1 Note: The small circle denotes optionality (a person need not be a customer; but to be a customer, he or she must rent at least one tape) 24 1From: Rob, P.; Coronel, C. Instructor’s Manual to Accompany Database Systems: Design, Implementation, and Management. Fourth Edition. CD-ROM © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

Crucial Use of E-R Analysis (2) 5/18/2019 Crucial Use of E-R Analysis (2) The typical resolution of many-to-many (M:N) relationships is by a bridge table (also called a composite entity) 25 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

Crucial Use of E-R Analysis (3) 5/18/2019 Crucial Use of E-R Analysis (3) A further explication of the resolution of the M:N relationship 26 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

27 Discussion Questions T/F ERD supports generalization. 5/18/2019 Discussion Questions T/F ERD supports generalization. Cardinality of one is symbolized by a bar -- | --written across the relationship line. An entity type must have at least one relevant attribute type. Entity Type Name is Synonyms and Homonyms. Cardinality: A business rule indicating the number of times a particular object or activity may occur. 27 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad

5/18/2019 Tasks for Next Lecture Task 1: Team forming – Team name, Team members’ names (2-3) per team, and team members’ e-mails Task 2: Contact information – Email your name, e-mail, and phone # Task 3: Practical exercise: ERDs Task 4: Assignment #1 28 © 2003-2006 Dr. M.E. Fayad SJSU – CmpE --- M.E. Fayad